The long-term goal of this research is to define cellular and molecular pathways which signal and regulate compensatory growth of the lung following pneumonectomy (PNX). In many species partial lung resection initiates rapid hyperplastic growth of the remaining lobes to restore normal tissue mass, cellular ultrastructure and physiological function. Previous work described the time course and nature of the response to PNX, and defined its regulation by factors such as age, growth hormone and adrenal steroids. Although morphometric data show that all cell types of the alveolar region grow and divide after PNX, little data pertains to the cellular details or to the molecular basis of the response. It is proposed to apply the techniques of cellular and molecular biology to address these issues. We propose to identify early changes in gene transcription which precede or accompany compensatory growth, to localize these changes to specific lung cell types, and to relate these changes to physiologic regulatory signals which may underlie initiation and progression of compensatory growth. The approach involves four specific aims: 1. To identify rapid early changes in gene expression which precede and accompany the compensatory increase in lung mass following PNX. Subtractive hybridization will be used to identity new mRNA transcripts which appear selectively during the early post-PNX interval; parallel changes in proto-oncogene expression also will be characterized. 2. To localize newly-expressed mRNA transcripts to specific cells of the lung parenchyma and thus to identify the cell type(s) affected most rapidly following PNX. Using in situ hybridization, cDNA probes against selected gene transcripts will localize and identity the responsive cell population(s). 3. To evaluate whether factors proposed to initiate compensatory lung growth in vivo elicit rapid changes in transcription of the same genes under controlled in vitro conditions. Using isolated perfused lungs and cultured lung cells, physical and/or soluble signals postulated to initiate compensatory growth will be tested independently to determine acute effects on gene transcription at the tissue and cellular levels. 4. To determine whether the early post-PNX events described above are modified under conditions which accelerate compensatory lung growth. Lungs and/or cells from adrenalectomized animals will be tested in vivo and in vitro to evaluate the effects of adrenal steroids on early gene transcription. These experiments will address whether hormonal regulation of compensatory growth is exerted concomitant with the primary growth signal, or at a later stage of the response. This approach will identify specific cells which respond rapidly to the signals which initiate compensatory growth; extend these observations to address the regulatory aspects of the response; and identify specific changes in gene expression which may be essential to growth of the lung. The results will provide a basis for more detailed future studies of physiologically significant pathways which signal and control normal lung growth, and which may in a more broad context pertain to the growth of other tissues.